This invention relates to an apparatus for soldering printed circuit boards.
To reply to recent demands for compact electrical appliances and instruments, there is a tendency of using small thin chip type electric parts for mounting on the printed circuit boards in place of the conventional discrete type electric parts. From the view point of the parts mounting operation, the chip type parts also excel the discrete type parts in that the former can be fixed on a board by face bonding and can be mounted in positions automatically in a facilitated manner and at a lower cost whereas the latter parts are difficult to insert into through holes of the printed circuit boards by automatic operation and involves an increased number of steps, for example, a step for cutting lead wires depending from the underside surface of the board.
Although there have thus far been proposed various soldering apparatus for printed circuit boards, they invariably give rise to problems of soldering failures when applied to printed circuit boards bearing the chip type parts due to the recesses defined between adjacent chip type parts or behind the chip type parts as seen in the direction of travel of the boards. Such recesses or space can block the molten solder from flowing thereinto and can trap gases therein, causing incomplete deposition of the solder. The air bubbles once trapped in the recesses are difficult to remove even if the printed circuit board is contacted with the molten solder for a long period of time.